Colour Tools for Painters

by Paul Centore

This website is devoted to applying colour science to everyday problems that
painters face. The goal is to provide, as far as possible, a rigorous understanding
of the use of colour in painting. Although justifications for the results can
be highly technical, the results are presented non-technically wherever possible,
with an eye to practical employment by artists. An important tool is the Munsell Colour System,
devised by the painter Albert Munsell at the turn of the 20th
century. The Munsell system's concepts of hue, value, and chroma, are basic
to painting, and provide a convenient framework for colour decisions in painting.

A Munsell-Accurate Value Scale

Value scales, or grey scales, that show how light or dark a colour is, are helpful for
artists and designers (and quilters, too). The scale pictured below is the result of a project
to produce an economical, finely gradated, Munsell-accurate tool to identify the Munsell values of
colours and to mix paints of a desired lightness. It is
available on Amazon.com
for less than $10.

Shadow Colours

A scientific analysis of the colours of an object in shadow, relative to
the colours of that same object in light, has led to two simple tools that realistic
painters can use when depicting shadows. The first is a simple visual rule, expressed
in terms of the Munsell system, and illustrated on the left.
A PDF file with a detailed, non-technical explanation and examples,
Shadow Colours For Painters, can
be downloaded. The second tool appears in
Consistent Shadow Values For Painters,
which presents the visual aid shown below on the right. Painters can use this aid when
representing objects of different
colours in the same illumination.

An Example of Shadow Colours in the Munsell System

Visual Aid for Consistent Shadow Values

Colour Analysis of Artists' Pastels

Most pastel companies produce hundreds of pastels, of different colours. Painters need
some organizational system, and some measured data, to use pastels effectively. This
need is particularly acute when buying pastels sight unseen, because electronic and
catalogue reproductions of pastels' colours are usually inaccurate. The page
Colour Analysis of Pastels
presents such results for eight pastel brands, in the reports
Pastels: A Colour Guide For Artists and Manufacturers. A more technical discussion of
the pastel gamut is given in
A Colour Survey of Artist's Pastels.
One interesting result is the discovery of duplicates, or pastels of
the same brand whose colours are nearly identical. The figure below shows some duplicates
for Rembrandt pastels.

Some Duplicates in Rembrandt Pastels

Producing Munsell Colours Electronically

Since many colour examples and discussions occur over the internet, it is helpful to
have a method for producing Munsell colours electronically. The sRGB system is a
colour standard for computer monitors and other display devices. When an
sRGB-compliant device uses an RGB triple to display a colour, the properties of
that colour conform to a colorimetric, device-independent specification. As a
result, the same RGB triple should always produce the same colour, even
though it is displayed on
different sRGB-compliant devices. The Munsell system also conforms to a
colorimetric specification, called the Munsell Renotation. Both systems specify
ambient lighting conditions for viewing, but the sRGB system uses Illuminant D65 lighting,
while the Munsell system uses Illuminant C lighting. The article
Conversions Between the Munsell and sRGB Colour Systems provides a set of
tables that specify which sRGB values produce desired Munsell
colours on a computer monitor. To account for the differences between Illuminants
C and D65, the monitor should be viewed in a
room lit by indirect daylight.

Consultations and Contact Information

I am available on a freelance basis for
consultations involving colour, from both the
artistic and scientific points of view. Comments, criticisms, suggestions, and questions
are welcomed on any of the topics covered by this website. I can be reached by email at
xxxpaul@xxxisletech.xxxnet (leave the x's out of the address).

Colour Science

Though this site presents easily applied, and therefore non-technical,
procedures for painters, the procedures have highly
technical origins. Much of the development relied on Octave/MATLAB computer code written
by myself, and assembled into the open-source
Munsell and Kubelka-Munk Toolbox. Other researchers are invited to correct,
modify, and extend this code, with the understanding that they will make their
modifications and extensions freely available. The process of developing tools for
artists led into many aspects of colour science. The page
Colour Science Papers
presents some peer-reviewed publications that resulted, along with more expository writings.